In quantum mechanics, among plasma waves of free electrons in metal, a plasma wave localized on the surface of metal is called surface plasmon. The surface plasmon is a mix of a plasma wave and an electromagnetic wave, and is transmitted along the surface of metal. In recent years, attention has been drawn to a technique of measuring materials located on the surface of metal by applying, by means of light, resonance-excitation (generation) to the surface plasmon. This measurement technique using the surface plasmon resonation (SPR) is noted in that interaction of biological material, such as protein, can be measured without chemically modifying pigment, etc., and that dynamic behaviors in the interaction can be grasped at high precision in real time.
A conventional plasmon sensor apparatus 10 using the above-mentioned measurement by SPR (hereinafter, referred to as “SPR apparatus”) is shown in FIG. 19. The SPR apparatus 10 includes: a SPR sensor 1 formed at the fore end portion of a optical fiber 2; a light source 3 for emitting a light having a predetermined wavelength or frequency so as to output the light, via the beam splitter 4 and the fiber coupler 5a, to the SPR sensor 1; and a light detector 8 for detecting, via the beam splitter 4 and the fiber coupler 5a, a reflected light (light information) reflected at the SPR sensor 1. As the light source 3, a He—Ne laser light source or a halogen lamp is employed, whereas as the SPR sensor 1, a sensor of a frequency-variable type is employed because measurement is basically performed while keeping an incidence angle constant. Also, when using polarization, polarizing elements 5b, 5c, such as a ½ wavelength plate and a ¼ wavelength plate, are provided.
In the conventional SPR sensor apparatus 10 shown in FIG. 19, light emitted from the light source 3 is transmitted through the beam splitter 4 to be projected onto the measurement surface 6 of the SPR sensor 1 via the optical fiber 2. When the light is irradiated on the measurement surface 6, reflected light is generated at the measurement surface 6 and is introduced via the optical fiber 2 and the beam splitter 5 into the light detector 8. The reflected light supplied from the measurement surface 6 has a property that the intensity of the reflected light changes when a measurement object material 7, flowing in the direction shown by the arrow in the drawing (left to right facing the sheet), joins the measurement surface 6. Accordingly, by measuring the change in the intensity of the reflected light, a property and reaction of the measurement object material 7, and further the interaction between materials, etc. can be measured in real time.
Patent document 1: Japanese Patent application laid-open publication No. 2001-165852